1. Field of the Invention
This invention relates to the testing of integrated circuits or other items having a pattern of contacts thereon.
2. Description of Related Art
Integrated circuits or chips are manufactured with large numbers of identical circuits on a single wafer which ultimately are separately cut from the wafer for use. It is necessary to test each circuit individually to determine whether or not it functions as intended before separating it from the wafer.
Conventional testing employs a probe card which is provided with a large number of small tungsten blades or needles that are mechanically and electrically connected to a circuit board and act as contacts. Electrical leads extend from the contacts to the outer edge of the board for connecting the probe card to test circuitry. In use, the blades or needles are moved into engagement with the pads of an integrated circuit. This provides an electrical connection so that signals can be read to determine the integrity of the circuit on the chip.
The needles or blades must all fall in the same plane in order to assure that each one makes electrical contact with a pad of the integrated circuit. This is accomplished by bending the blades or needles after they are mounted on the probe card, which is laborious, time consuming and expensive. Even after such adjustment the blades or needles tend to creep back toward their original positions so that their adjusted locations are lost. This loss of adjustment also comes about from the pressure of the needles against the chips, aggravated by the scrubbing action used to assure penetration of any oxide coating. As a result, constant maintenance is necessary or the probe cards will not perform their intended function. Even when in proper adjustment, the needles cannot compensate for significant differences in the heights of the contact pads on the integrated circuit chips being tested. The needles also may apply excessive forces against the chips so as to damage the chips. The close spacing necessary for testing some chips cannot be achieved with conventional needle contacts.
An improved testing arrangement is disclosed in co-pending application Ser. No. 606,676, filed Oct. 31, 1990, by John Pasiencznik, Jr., now U.S. Pat. No. 5,148,103 for METHOD AND APPARATUS FOR TESTING INTEGRATED CIRCUITS assigned to the same assignee as that of this application. This prior application is incorporated herein by reference as though fully set forth. In this prior arrangement, a flexible membrane is provided with raised features on one side which connect through circuit traces to a probe card that, in turn, is connected into the test circuit. Air pressure is used to deflect the membrane as the contacts of the membrane are pressed against the pads of an integrated circuit to provide an electrical connection. There is room for improvement, however, in assuring that adequate pressure exists between the contacts on the membrane and the pads on the integrated circuit chip to assure a good electrical connection, while at the same time avoiding undesirable contact between remaining portions of the membrane and the chip.
The amount of pressure on the membrane in the earlier design is limited by its physical characteristics which in turn limit its ability to engage contacts on the chip which are not in the same plane. Advancement of the chip toward the membrane merely will deflect the membrane inwardly rather than causing all of the contacts to make engagement in some instances. Excessive drape of the membrane around the contacts may result. The membrane will be deflected to such an extent that it undesirably engages the chip around the contact rather than engaging only at the contacts.